Finding the Lowest Common Denominator
Step 1: See if the smaller denominator divides into the larger denominator with no remainder.
Say we want to add:
Because 9/3 = 3, the lowest common denominator is 9. After that we do:
because 3/3 = 1. Then we replace 1/3 by 3/9 in the problem.
Step 2: If step 1 doesn't work, we use the Euclidean Algorithm to first find the largest divisor of both numbers. Say we add:
using the Euclidean Algorithm, we find that 3 is the largest divisor of 12 and 9. We then follow these steps:
1. Divide the first denominator by 3.
2. Multiple the second fraction by 4/4 because 4 was the answer from the division.
3. Divide the second denominator by 3.
4. Multiple the first fraction by 3/3 because 3 was the answer from the second division.
5. Add the two fractions with the common denominator.
What do you need help with? Click on one of the following topics...
What is a fraction?
Subtracting a fraction from a whole number
Multiplying a fraction and a whole number
Dividing a fraction and a whole number
What is a reciprocal?
Changing a fraction to a percentage
Changing a percentage to a fraction
Rounding to a whole number
Finding the lowest common denominator
Reducing a fraction
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